A self-bearing motor (SBM) is an electric motor with a magnetically integrated bearing function, that is, it can provide levitation and rotation simultaneously as a single actuator. This paper presents the design, operating principle and control system for the slotless self-bearing motor (SSBM). In this design, the stator has no iron core but includes six-phase coils. The rotor consists of a permanent magnet and an enclosed iron yoke. Magnetic forces generated by the interaction between stator currents and the magnetic field of the permanent magnet are used to control the rotational speed and radial position of the rotor. In this paper, the torque and radial bearing forces are analyzed theoretically with the aim to develop an improved control system. In order to confirm the proposed control method, an experimental system was constructed and tested. Simulation and measurement results show that the SSBM can work stably in modes such as start, reverse, rotation load and external radial pulse forces.
The disturbance and uncertainty of the motor drive systems are very complicated terms. There is no exception for the slotless-self bearing motor (SSBM), where the perturbations of the bearing motor are mainly came from the outside as the wind affect, from inside as the thermal changing of the coils, and incorrect modeling of the winding processes. First, to delete these inversed terms, this paper proposes a new super-twisting disturbance observer (STDOB) to obtain the desired goal of the robust control design. The proposed disturbance observer was based on the information of measured and estimated states with the aim of softening the cost of the measurement. Second, to estimate the velocities and accelerations of the movements on x and y axes, the stability concept of homogeneous function-based was used to design the fixed-time state observers (FTSOBs) for these axes. The state of the rotational operation on axis was estimated with a fixed-time state observer. Third, to control the positions and rotational speed, a variable boundary layer thickness (VBLT) fixed-time sliding mode control (FTSMC) was designed to force these positions and speed states converge to the desired goals. Finally, the stability of the proposed control algorithm was theoretically verified by using Lyapunov condition and simulation of MATLAB software. The obtained states were acceptably stable with small overshoots, small settling-times, and stable steadystates.INDEX TERMS Slotless-self bearing motor, super-twisting disturbance observer, variable boundary layer thickness, fixed-time sliding mode control.
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